1. Field of the Invention
The present invention relates to a process for the production of fermented milk products.
2. Description of the Prior Art
Fermented milk products, such as curdled milk, yogurt and cultured buttermilk, are characterized on the one hand by an acidity and aroma produced by lactic-acid bacteria and on the other hand by a thick consistency. In products to be eaten with a spoon, the structure is gel-like, sometimes stretchy, and in products to be drunk it is semifluid, possibly stretchy. In both principal types of products, the aim is to obtain a stable structure in which the whey does not separate from the curd.
The structure of fermented milk products prepared in the conventional manner without additives such as stabilizers is obtained by a strong heat treatment of the raw milk, in practice at above 90.degree. C. for 5-30 minutes. The soluble proteins, the so-called whey proteins, of the milk are thereby denatured. Their colloidal properties change in such a way that they, together with the casein of the milk, take up significantly more of the water of their surroundings than they do in the undenatured state. After lactic-acid fermentation, the typical structure of the products forms. In some cases the structure is also affected by capsules formed by lactic-acid bacteria around themselves. Whether the product will be eatable with a spoon or drinkable is determined by the method of ripening.
Since the heating required for producing the structure of the product is of long duration, the energy-efficient plate heat exchangers which are commonly used for the pasteurization of milk and by means of which a regeneration of over 90% is achieved, cannot be used alone.
In process technology, the traditional heat treatment stage for fermented milk products is realized by means of a long-duration heat treatment. The apparatus required for this can be, for example, either a closed cylinder or series of cylinders coupled in a position following the heating compartment of the plate heat exchanger, the required long-duration heating being achieved in its flow expansions, or a processing tank coolable to the fermentation temperature. In these, losses of heat are significant.
As regulation and control techniques become more advanced, the aim is, for reasons of cost and operational reliability, to carry out dairy processes and important washing and sanitizing steps in a programmed manner under remote control or automatically. The current long-duration heating systems for fermented milk products, with their flow expansions, constitute obstacles to the most economical applications of regulation and control systems.